Video coding using multi-resolution reference picture management

A video coding apparatus comprising:

• a memory;
• and
• one or more processors coupled with the memory and configured to:
• obtain a list of reference pictures comprising a plurality of pictures, wherein the plurality of pictures comprising at least a first picture with a first spatial resolution, and a second picture with a second spatial resolution different from the first spatial resolution;
• obtain a reference picture from the list of reference pictures;
• and
• code a current picture by using the reference picture with its original spatial resolution without ensuring the reference picture to have a same spatial resolution as the current picture;
• wherein the one or more processors are further configured for obtaining one or more syntax elements indicative of a picture width and a picture height for each picture of the plurality of pictures in a picture parameter set (PPS);
• and
• wherein the current picture is coded with a third spatial resolution based on the reference picture of the list of reference pictures, and wherein a ratio is determined based on the third spatial resolution and a spatial resolution of the reference picture for coding the current picture.

A non-transitory computer readable medium storing instructions and a bitstream, wherein the instructions when executed by one or more processors, cause the one or more processors to perform operations to generate the bitstream, the operations comprising:

• obtaining a list of reference pictures comprising a plurality of pictures, wherein the plurality of pictures comprising at least a first picture with a first spatial resolution, and a second picture with a second spatial resolution different from the first spatial resolution
• obtaining a reference picture from the list of reference pictures;
• and
• coding a current picture by using the reference picture with its original spatial resolution without ensuring the reference picture to have a same spatial resolution as the current picture;
• wherein the operations further comprise:
• obtaining one or more syntax elements indicative of a picture width and a picture height for each picture of the plurality of pictures in a picture parameter set (PPS);
• and
• wherein the current picture is coded with a third spatial resolution based on the reference picture of the list of reference pictures, and wherein a ratio is determined based on the third spatial resolution and a spatial resolution of the reference picture for coding the current picture.